The maturity method: Modiﬁcations to improve estimation of concrete strength at later ages Yahia A. Abdel-Jawad Civil Engineering Department, Faculty of Engineering, Jordan University of Science and Technology, P.O. Box 3030, Irbid, Jordan Received 11 August 2004; received in revised form 10 March 2005; accepted 30 June 2005 Available online 19 August 2005 Abstract Two modiﬁcations have been proposed for the Nurse–Saul maturity function to get better estimates of compressive strength of concrete cured at diﬀerent temperatures. The modiﬁcations account for the eﬀect of w/c ratio on the temperature dependence of strength development and the eﬀect of curing temperature on the long-term strength. The eﬀect of the proposed modiﬁcations on the estimation of concrete strength using the Nurse–Saul maturity function have been compared with the estimation using unmodiﬁed Nurse–Saul equation with two diﬀerent datum temperatures (i.e., T 0 = 10 °C and T 0 =0 °C). The results show that applying the proposed modiﬁcations improves the accuracy of estimated concrete strength at diﬀerent curing temperatures, espe- cially at later ages. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Maturity; Nurse–Saul; Curing temperature; Compressive strength; Concrete; Mortar; Strength development 1. Introduction During the last decades, the maturity method has been developed and used as one of the most favorable methods for estimating in-place concrete strength. The in-place strength is estimated based on the in-place maturity index and a previously established relationship between maturity index and strength [1–5]. In 1987, ASTM adopted a standard practice on the use of the maturity method to estimate in-place strength (ASTM C 1074). This standard permits the user to ex- press the maturity index either in terms of the tempera- ture–time factor using the Nurse–Saul equation or in terms of the equivalent age at a speciﬁed temperature using the Arrhenius equation. Using the Nurse–Saul equation, the temperature– time factor is computed as follows: M ðtÞ¼ X ðT a  T 0 ÞDt; ð1Þ where M(t) is the temperature–time factor at age t; de- gree-days or degree-hours; Dt is a time interval, days or hours; T a the average concrete temperature during time interval, Dt, °C, and T 0 is the datum temperature, °C. According to ASTM C1074-98 [6], it is recom- mended that the datum temperature be determined experimentally or may be taken as 0 °C if ASTM Type I cement is used without admixtures and the ex- pected curing temperature is within 0 and 40 °C. How- ever, the T 0 value used for decades and still used by most maturity instruments is 10 °C, which is approx- imately the temperature at which the hydration of ce- ment ceases. Using the Arrhenius equation, the equivalent age at a speciﬁed temperature is computed as follows: t e ¼ X t 0 exp  E R 1 T a  1 T s      Dt; ð2Þ 0950-0618/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2005.06.022 E-mail address: jawad@just.edu.jo. Construction and Building Materials 20 (2006) 893–900 Construction and Building MATERIALS www.elsevier.com/locate/conbuildmat